1. Field of the Invention
The present invention relates to a light-emitting diode for emitting a visual light or an infrared light, and which may be used for vehicle lamps, indication lamps, light communication apparatus and sensors, and as a light source.
2. Description of the Prior Art
A known light-emitting diode of this type is shown in FIG. 7. In the known light-emitting diode, reference numeral 1 denotes a light-emitting element of the GaP or GaAsP type. The light-emitting element 1 is mounted in a recess portion 2a of one lead frame 2 and is connected to the other lead frame 3 by a wire 4 using a bonding method. Then, the light-emitting element and the lead frames are integrally molded with resin and there is provided a positive lens portion 5. The front end of the lens portion 5, i.e., the end surface 5a from which light is emitted, is formed in a spherical configuration in order to obtain a parallel light bundle of light rays along an optical axis X.
In the light-emitting diode of FIG. 7, the angular region over which the light emitted from the light-emitting element 1 can be parallel on the spherical end surface 5a, is .theta..sub.1, about 60.degree.. A reflective plating is provided at the inner surface of the recess portion 2a of the lead frame 2. Therefore, the light emitted from the light-emitting element 1 to the side direction is reflected to the forward direction, as shown in FIG. 8. In FIG. 8, the solid line shows the light emitted from the center of the light-emitting element 1, while the dash line shows the light emitted from the side of the light emitting element 1. The light within the region .theta..sub.2 (about 20.degree.) can be reflected in the forward direction, thereby providing an effective light for illumination. Therefore, the angular region for providing the effective light directed forwardly is, as a whole, .theta..sub.1 +2.theta..sub.2. The other angular region .theta..sub.3 (about 40.degree.) is never used to provide effective light.
Referring to FIG. 9, a directivity characteristic of the light-emitting element of GaP and GaAsP types is shown as the curve 6. The region in which effective light can be obtained is within the angle .theta..sub.1, over which the light emitted from the light-emitting element 1 is directed in the forward direction and the angle .theta..sub.2, over which the light emitted from the light-emitting element 1 is in the side direction. However, the luminance from the angular region .theta..sub.2 is extremely small. Therefore, even if the light within the angular region .theta..sub.2 is effectively utilized for illumination, it is not expected to make the illumination increase substantially. A reflection at the recess portion 2a in FIG. 8 is considered in that the diameter of the aperture of the recess portion 2a is about three to five times as large as that of the light-emitting element 1. Further, the light-emitting element 1 usually emits a light from the entirety of light-emitting element 1. Therefore, the light-emitting element 1 is not considered as a point light source. Thus, the light reflected from the recess portion 2a is in actuality directed almost to the ineffective direction. Therefore, even if the reflection surface of the recess portion 2a is utilized, the light reflected from the recess portion 2a is relatively little. Furthermore, the light emitted from the light-emitting element 1 within the angular region .theta..sub.3 having a high luminance is not utilized at all. Therefore, the construction of FIG. 7 is not expected to increase substantially the illumination of the light-emitting diode on the whole.